The present invention relates to the field of electronic circuits. Specifically, embodiments of the present invention relate to an improved method for generating parameters for causing a voltage-controlled oscillator to operate at a desired frequency.
Conventional wireless transceivers use a phase locked loop (PPL) having a voltage controlled oscillator (VCO) for establishing a carrier frequency. A conventional wireless transceiver may be required to operate at many different carrier frequencies, depending upon which channel a user desires to operate and other factors. For example, there may be a number of channels each a with carrier frequency at a specific frequency between a range from 2.4 GHz to 2.8 GHz.
The carrier frequency may be based off the output of the VCO, so to create the appropriate carrier frequency the frequency of the VCO is adjusted. In order to accurately adjust the VCO, typically a signal output by the VCO is divided in frequency and compared to a reference signal by a frequency and phase detector. Based on the comparison, the VCO""s frequency is adjusted up or down so that the target carrier frequency is achieved from the VCO output signal.
Conventionally, when the VCO signal""s frequency is divided down, the frequency is scaled according to a precise timing pattern. For example, the frequency may be scaled by a first factor for xe2x80x98xxe2x80x99 cycles and then by a second factor for one or more cycles. In this fashion, the VCO signal is divided to a very precise frequency. In order to trigger which frequency scaling factor used, conventional techniques produce a counter value that is appropriate for the desired carrier frequency. When the counter reaches zero, the frequency scaling factor is changed.
Conventionally, a second counter value is used to produce a feedback signal from the frequency scaled signal. The feedback signal Is then compared to a reference signal. Conventionally, the second counter is used to determine when the frequency divided signal is fed back to a phase and frequency detector to be compared to the reference signal. The conventional method must have a way of producing a second counter that will produce the feedback signal at the appropriate time to correctly adjust the VCO such that the desired carrier frequency is produced.
A first conventional technique for producing the first and second counters is a lookup table containing first and second counter values corresponding to each of the possible carrier frequencies. This table can be very large as not only are there separate carrier frequencies for different broadcast channels, but a given broadcast channel typically may have multiple carrier frequencies based on a variety of factors such as local broadcast regulations. Unfortunately, the lookup table can consume considerable area on the transceiver chip. When area is at a premium, this solution is very costly.
A second conventional solution is to use a processor to generate suitable counter values. However, the generation of proper values is not trivial. Thus, this solution is costly from a standpoint of consuming valuable processor cycles. In applications in which processor cycles are precious, this solution is undesirable. Thus, a need exists for a method for adjusting the frequency of a VCO that does not consume valuable processor cycles or chip space with look up tables or the like. A further need exists for a method of generating a carrier frequency that does not consume valuable processor cycles or chip space with look up tables or the like.
Embodiments of the present invention provide a method and device for adjusting the frequency of a VCO that do not consume valuable processor cycles or considerable chip space with look up tables or the like. Embodiments of the present invention provide a method and device of generating a carrier frequency that do not consume valuable processor cycles or considerable chip space with lookup tables. Embodiments of the present invention provide these advantages and others not specifically mentioned above but described in the sections to follow.
Embodiments of the present invention provide a method and device for generating parameters for adjusting the frequency of a VCO. A desired carrier frequency may be based off the output of the VCO. A method embodiment for generating parameters for adjusting the frequency of a VCO comprises receiving a channel number. The method determines a first parameter that is operable to adjust the frequency of the VCO, based on the channel number. The method also determines a second parameter operable to adjust the frequency of the VCO, based on the channel number. The first parameter may be used to select a frequency scalar in a closed loop with the VCO. The second parameter may be used to provide a feedback signal to adjust the frequency of the VCO.
The above method may further include inputting the channel number into combinatorial logic to determine the first and second parameters. The method may still further include adding one or more offsets to the channel number before determining the first and second parameters, wherein the frequency of the VCO is further adjusted based on the offset(s).
Another embodiment of the present invention is a device for adjusting the frequency of a VCO. The device comprises logic that is operable to receive a channel number and to produce oscillator adjustment parameters based on the channel number. The device also includes registers for receiving the oscillator adjustment parameters. The parameters may be used to select a frequency scalar in a closed loop with the VCO and to provide a feedback signal to adjust the frequency of the VCO.
The device may further comprise a register coupled to the logic that is operable to hold an offset to add to the channel number. In this fashion, the frequency of the VCO may be further adjusted, based on the offset in the register.
Another method embodiment is for producing a signal having a desired carrier frequency. This method includes receiving a channel number and inputting the channel number into combinatorial logic to determine a plurality of parameters that are operable to adjust the frequency of a VCO, based on the channel number. The plurality of parameters are applied in a circuit comprising the VCO to adjust the frequency of the VCO to produce a desired carrier frequency that is derived from the VCO.